Present invention relates to a method for reading the codes, as well as a method for creating for hidden coding on an object.
At the present several methods are known for automatic collecting of data, as barcode, radio frequency identification and data communications, magnet strips and OCR-systems.
In the last years it is developed two dimensional codes in addition to linear bar codes. One such code is Data Matrix, which is a public available and accepted digital code and which is specially used within the electronics, pharmacy, and car industry. The codes may be printed, written by ink jet printers or stamped in a product. By a video camera system the code may be read and interpreted. Partially advanced image processing routines and illuminations techniques have to be applied to secure an interpretation of the codes which are impressed on the product.
In many application cases it may be desired to hide the codes, e.g. in data collection as a part of computerized, integrated production where the surface is worked on current production process. The possibility to be able to document the origin, condition of production, and secure the quality is important for many manufacturers, which is provided by marking a product in order to track and/or retrieve the above mentioned information. In order to accomplish this is a hidden code desirable, which not create visible marks on the product and therefore do not disappear by working the surface and thus makes it possible to obtain information about a product and where in addition is obtained assurance against pirate copied products as a such marking, which may be encrypted, will be difficult to copy.
The code may be created in the material and covered by normal surface finishing, as varnish/painting, plastic, laminate, wood or metal. The code may be stamped from the material, eventually represented by a thin film which is attached to the material and covered and thereby hidden.
The code may according to present invention be read by means of ultrasound. EP 0 460 733 A1 corresponding to Norwegian paten application no. 1991 2084 describes a system for marking and then especially devices in connection with oil well boring. The system is comprised of an identification plate comprising a number of holes, indentations and the like, where these is extending partly through the plate. The holes/indentations may be formed in a two dimensional data code similar to the Data Matrix code. This plate is mounted on the utility which is intended to be marked in such a way that the surface of the plate comprising said holes/indentations is hidden. Marks in form of holes/indentations is read by means of ultrasound.
The herby known system used principal for reading codes uses, however, a principal which maybe compared with a wave focusing which have strong demand to the wavelength in respect of the thickness of the covering and dimension of the holes/indentations and which therefore do not make the method especially well suited for working on the surface as the changes may lead to reduction of the thickness of the cover by the working of the surface, which may result in that the chosen wavelength comes out of focus and thereby may a diffraction of the reflected waves arise which make a detection of the holes/indentations impossible.
Said hiding of the codes are however not very appropriate by a product where the objects aesthetic outlook is of importance as the attachment of a plate to a product will be associated with a substantial interference in the outer of a product if a such device not shall be visible, e.g. will it be necessary with a milling of a cavity in the product corresponding to the plate with the code and thereafter processing of the welding seams by welding of the plate to the product, thus a work intensive process.
The present invention is intended to avoid the above mentioned drawbacks and in addition render possible creation of the hidden code as part of the normal processing of a product, which is provided by means of a method for reading the codes, as well as a method for creating hidden coding on an object.